Process of dyeing cotton fibers with indigo vat dyes



J. M. FIELDS July 22, 1969 PROCESS OF DYEINQ COTTON FIBERS WITH INDIGOVAT DYES Filed Dec.

2 Sheets-Sheet l INVENTOR. JESSE M. FIELDS July 22, 1969 J. M. FIELDS3,457,022

PROCESS OF DYEING COTTON FIBERS WITH INDIGO VAT DYES Filed Dec 2, 1964 2Sheets-Sheet 2 65 ROI O. '0

FIG. lc

INVENTOR. JESSE M. FIELDS United States Patent US. Cl. 8-28 3 ClaimsABSTRACT OF THE DISCLOSURE The method of continuously applying hotindigo initially as a bottom dye and the continuous application of acold indigo dye as topping dye to obtain color intensity andpenetration.

This invention relates to the treatment of cotton fibers or cotton warpyarns with indigo dyestuif and t0 the method of continuously applyinghot indigo initially as a bottom dye and the continuous application of acold indigo dye as a topping dye to obtain superior color intensity andpenetration.

The application of indigo dyes to cotton and particularly to denim isquite well known in the dye art. However, heretofore in the continuousdyeing systems for cotton warp yarns it has been conventional to employa series of vats including an initial vat for boil off and another vatfor rinsing with subsequent vats of cold indigo dye being utilized withthe number of dips varying according to the depth of shade and to theconcentration of the vat. A larger number of dips in weak vats yieldsfaster dyeings than less dips in strong vats with the cotton yarns beingimmersed in the vat for a period sufficient forthe liquor to penetratethe fiber after which the material or yarns, after squeezing, is airedor skyed through the atmosphere for reoxidation and color development.The airing or skying between dips in cold indigo vats as well as dips incold water after the dips in indigo will usually increase the rate ofoxidation or reoxidation of the indigo ultimately to obtain the desiredshare or color intensity.

Penetration of cold indigo dyestuff has been found to be limitedseverely as exemplified in denim fabrics that have been subjected toabrasion tests revealing that the core or inner portion of the fibers ofthe cotton yarn do not absorb uniformly the dyestuff as the penetrationinto the inner fibers or core of the yarn is apparently limited whetherdue to the lack of dye penetration or for the reason that thesuperficial penetration precludes or serves as a filter against furtheror increased indigo penetration. This feature is exemplified by theconsiderably lighter shade in the interior of the cotton yarn that issubjected to abrasion testing. Therefore, various processes have beenattempted to achieve more efficient or increased dye penenation toobtain not only the desired shade but also increased penetration of thefibers so that upon wear the lack of dye penetration into the depth ofthe yarns will not exhibit non-uniform color penetration and that thewhite core will not grin through the surrounding colored yarn or fibers.

The present invention has as one of its objectives the application of acontinuous process for applying hot indigo dyes for maximum yarnpenetration as a bottom dye and 3,457,022 Patented July 22, 1969 "icethereafter subjecting the yarns to a cold indigo solution as a top dyeto obtain the desired dye penetration, achieve ultimate shade or colorintensification and penetration.

Another objective of this invention is to obtain increased indigopenetration of cotton fibers by utilizing a continuous dyeing system inwhich hot indigo is employed as a bottom dye through a series of hotdips in a continuous path of travel of the yarns and then subjecting thehot indigo dipped yarns to a series of cold indigo dips withintermediate airing or skying for oxidation and reoxidation.

Still another objective of this invention is to provide a process andproduct in which a hot bottom indigo dye is applied to cotton fibers forincreased dye penetration to achieve fast color fabric characteristicsand a top cold indigo dye for optimum color intensification.

Yet another objective of this invention is to apply a continuous dyesystem method in which a series of hot indigo dye baths are utilized toachieve increased dye penetration followed by a series of cold indigodye bath dips applied at temperatures of less than degrees F. to obtainoptimum color intensification and penetration of the cotton fibers.

Other objectives and many of the attendant advantages of this inventionfor producing a penetrated vat dye indigo will become more readilyapparent to those skilled in the fabric dyeing art from the followingdetailed description taken in conjunction with one illustration of anapparatus which is schematically illustrated for employing thisinvention, and wherein:

FIGS. 1A, 1B and 1C are schematic or diagrammatic illustrations, insections followed sequentially, presenting one system of apparatusemploying the process of this invention for producing a cotton warp yarnhaving increased dye penetration and color intensity.

Briefly, the process employed for obtaining greater indigo dyepenetration to cotton warp yarns may be utilized with conventionalapparatus presently being employed and includes the introduction of thecotton yarns .that are traveling continuously through a series of hotindigo dye vats that are maintained at temperatures varying from thefirst vat of 160 degrees F. down to a vat at approximately degrees P.which will be within the range for applying the hot indigo to thecontinuously traveling yarns. Thereafter, the yarns may be introduceddirectly into a series of cold indigo vats arranged in series andmaintained at a temperature of 100 degrees F. or less with the number ofdips varying and depending upon the ultimate color intensity desired.Airing or skying between the hot indigo last dipand the introduction ofthe yarn to the first cold dip is a matter of choice but it has beenfound desirable to employ skying between successive cold dips to achievethe desired shade. After exiting from the last cold dip of indigo in astandard or normal charge, a series of cold rinses will be employedfollowed by a dip into a vat containing a suitable softener before thecontinuous yarns are dried by passing them over heated revolving drumsmaintained at a temperature of approximately 225 degrees F. to 240degrees F.

Referring to the drawings and particularly to FIG. 1A, there isillustrated schematically a flow diagram for cotton warp yarn 10 thatmay be unwound from a ball warp 11 wound on a beam with the yarn passingover roller 12 and guide rolls 13 with an intermediate compensating roll14 guiding the yarns into the first hot indigo bath 15 containedwithinthe vat or tank 16. The bath is a charge of indigo dyestuff preferablymaintained at a temperature of 160 degrees F. constituting the first dyebath to which the yarns are subjected. If desirable, a suitable boil offbox and succeeding rinse box may be employed prior to the yarns enteringinto the first dye box 16 as is conventional practice although it hasbeen found that very satisfactory results have been achieved without theuse of the conventional boil off and rinse boxes. As the yarns leave thefirst dye box 16, a pair of squeeze rolls 17 are rotatably mounted atthe exit of the dye box 16 to remove excess liquor from the travelingyarns which are subjected to a continuous pressure from the rolls beforethe yarns are introduced into the next dye box 18 in which there is asecond charge of hot indigo 19 that may be maintained at a temperatureof approximately 140 degrees F. The yarns will travel continuouslythrough the second dye box 19 by following a circuitous path of travel,in the same manner as in the first dye box 16 guided by the lower guiderolls 20 and upper guide rolls 21 before passing to the pair of squeezerolls 22 mounted for rotation at the exit end of the second dye box 18for removing excess liquor and returning it into the dye bath 19. Theyarns 10 will continue to travel and pass into the third dye box 23 inwhich there is also a charge of hot indigo similar to or substantiallysimilar to the dye charge in the dye boxes 16 and 18 with the dyesolution 24 being maintained at a temperature of approximately 120degrees F. The yarns will travel continuously through the dye box 23guided by the rolls 20 and 21 before exiting or leaving the dye box 23with the yarns passing between the squeeze rolls 25 for removing excessdye solution from the yarns and returning the solution into the dye bath24.

In the embodiment illustrated in FIG. 1A, a series of rollers 27 and 28guides the yarn from the hot indigo dye baths to the series of coldindigo dye baths permitting an intermediate stage for airing or skying,however, this intermediate stage may be eliminated entirely and thecontinuously traveling yarns may pass directly from the squeeze rolls 25mounted on the dye box 23 into the first cold indigo dye bath 29contained within the dye box 30. The yarns will be guided in theircontinuous flow within the dye box 30 by means of the rotatably mountedrollers 31 and 32 that are horizontally spaced from each other andvertically spaced to form a circuitous path of travel for the yarn in ahorizontal flight and in a vertical path through the dye box enablingthe yarns to exit and pass between the squeeze rolls 33 preparatory forskying directly above the dye box 30 guided by the vertically spacedapart rolls 34 and 35 during which skying the yarns having the coldindigo thereon will be oxidized. After leaving the first skyingoperation over dye box 30, the yarns will then be introduced into thesecond cold indigo dye box 36 in which there is also a normal orstandard indigo solution 37 similar to the charge in dye box 30. Theyarns will travel through the dye bath 37 and leave the dye box to passthrough the squeeze rolls 38 in the yarn path of travel to the skyingapparatus 39 directly over the dye box 36 with the yarn being guidedover the guide rolls in a similar manner as over the first cold indigodye box 30. The yarns traveling from the skying apparatus 39 will passinto, in sequence, additional dye boxes 40, 44, 47, 50, 53 and 56 inwhich normal or standard indigo charges 41, 45, 48, 51, 54 and 57 arecontained with the yarns passing from the cold indigo solutions that aremaintained at a temperature of 100 degrees F. or less and pass throughsqueeze rolls comparable to those shown in dye boxes 30 and 36preparatory for the skying apparatus 43, 46, 49, 52, 55 and 58.

After the requisite or desired number of cold dips, which may vary fromtwo to seven or eight, depending upon the desired shade, the yarns areintroduced into rinse boxes. Thereafter, the yarns are passed throughcold water rinses 58, 61, 64 and 67 contained in rinse boxes 57,

60, 63 and 66 with or without intermediate skying in the skyingapparatus 59, 62, 65 and 68. Ultimately the yarns are passed through asoftener solution 70 and 73 contained within vats 69 and 72 and may passthrough the skying apparatus 71 and 74 before the yarns are finallysubjected to a drying sequence over revolving heated drums that will drythe yarn and pass the yarn to a collection location.

One suitable solution for the hot indigo dye boxes used in dye boxes 16,18 and 23, is a charge of 300 gallons which will be heated to atemperature of 160 degrees F. and contains 12 /2 pounds caustic soda(50%), (liquid caustic); 5 pounds of sodium hydrosulfite (Na S O (hydropowder), 407 pounds of indigo stock liquor (41.5

gallons) a solution of reduced indigo, 12 /2 pounds of Tergitol 4 (orany other suitable wetting or penetrating agent). The charges in the dyeboxes 18 and 23 may be of the same materials but the temperature in dyebox 18 will be maintained at approximately 140 degrees F. and thetemperature in dye box 23 maintained at a temperature of approximately120 degrees F. It will be desirable to maintain a continuous feed ormake up for the dye boxes 16, 18, and 23 from a gallon solutionmaintained at a temperature of approximately degrees F. that is fed intoeach dye box containing 3 /2 pounds of caustic soda (50% liquid caustic)10 pounds of hydro powder, 215 pounds of indigo stock liquor (22gallons) and 4 pounds of Tergitol 4 with the remainder making up the 100gallons being water. Similarly in the 300 gallon charge, water will makeup the difference to form the charge.

In the stock formula for the normal solution contained in the coldindigo vats, a normal charge is formed of a diluted indigo and the stockmay be 8% indigo powder, 16% caustic soda (50% liquid) 6% hydro powderand 70% water in a volume of approximately 2,400 gallons which is fedapproximately every fifteen minutes to replenish the indigo.

It is desirable in at least one or both of the last vats 69 and 72 toemploy a suitable water dispersible softener.

It has been ascertained that abrasion tests conducted on cotton warpwoven into fabric to form denim that has been subjected to the bottomhot penetrating indigo dye and the top application of cold indigo dyehave revealed very substantial increased penetration of the dye into thecore of the cotton fibers.

Obviously many modifications may be made in the number of dips for thewarp in the hot indigo, the number of dips into the cold indigo withintermediate skying may also vary depending ultimately upon the desiredshade without departing from the purpose and spirit of this inventionand the illustrated example is not intended to limit the scope of theclaims appended hereto. Therefore, the process and product described forthis invention and variations thereof are contemplated within the scopeof the appended claims.

What I claim is:

1. In the process of dyeing cotton fibers comprising the steps ofapplying indigo at a temperature of from between degrees F. to .degreesF. to continuously traveling cotton yarns, applying indigo attemperatures below 100 degrees F. to the continuously traveling yarns inone or more dips to obtain the desired color intensity, and oxidizingthe indigo applied yarns after each indigo application by skying.

2. In the process of dyeing cotton fibers comprising the steps ofapplying indigo at a temperature of from between 150 degrees F. to 180degrees F. to continuously traveling cotton yarns, applying indigo attemperatures below 100 degrees F. in a series of sequential dips to thecontinuously traveling yarns, and skying the indigo applied yarns aftereach cold indigo dip application.

3. In the process of dyeing cotton fibers, comprising the steps ofapplying hot indigo at a temperature of from between 125 degrees F. to180 degrees F. to continuously 5 6 traveling eotton yarns by sequentialdips, applying indigo OTHER REFERENCES as a topping dye at temperaturesbelow 100 degrees F. to W Jacoby et al The Application of Vat Dyes,1953,

the continuously traveling yarns, and skying the indigo AATCC Pp 226430applied yarns after each of a series of sequential indigo dipapplications- 5 GEORGE F. LESMES, Primary Examiner References Cited T JHERBERT J A E UNITED STATES PATENTS R., ssistant xammer 2,110,595 3/1938Foss 8--38 US. Cl. X.R 2,920,932 1/1960 Barnhill 828 8542

